U.S. Trade Representative Lighthizer says goal is to complete talks this year

WASHINGTON—The Trump administration took the first step toward renegotiating the North American Free Trade Agreement, plunging into a battle that pits some Republicans and industry supporters of the pact against Democrats and some of the president’s most ardent backers.

In a letter to congressional leaders on Thursday, U.S. Trade Representative Robert Lighthizer said the administration would start talks on the 23-year-old deal in as...